Formation of α,ω-dienes upon photooxidation of alkenyl carbyne complexes

Article abstract of DOI:10.1016/S0022-328X(97)00262-3

Photolysis of the alkenyl carbyne complexes (η⁵-C5H5)(CO)Mo<*>CCH2(CH2)nCH=CH2 (n=2 (1b), 3 (1c) and 4 (1d)) in CHCl3 results in the formation of the corresponding α,ω-dienes CH2=CH(CH2)nCH=CH2.Also produced are the dichloromolybdenum

Full text of DOI:10.1016/S0022-328X(97)00262-3

Ž
.
Journal of Organometallic Chemistry 554 1998 13–18
Formation of a,v-dienes upon photooxidation of alkenyl carbyne
complexes
)
Karen E. Torraca, Damon A. Storhoff, Lisa McElwee-White
Department of Chemistry, UniÕersity of Florida, GainesÕille, FL 32611, USA
Received 2 December 1996; received in revised form 10 February 1997
Abstract
5
Ž
.Ž .Ä Ž
. 4
Ž
.
Ž
Ž
.
Ž
.
Ž
..
Photolysis of the alkenyl carbyne complexes h –C5H5 CO P OMe Mo'CCH2 CH2 nCH5CH2 ns2 1b , 3 1c and 4 1d
3
Ž
.
in CHCl3 results in the formation of the corresponding a,v-dienes CH2 5CH CH2 nCH5CH2. Also produced are the dichloromolybde-
num carbynes h –C5H5 Cl2 P OMe Mo'C–CH2 CH2 nCH5CH2 ns2 8b , 3 8c , and 4 8d . Both sets of products arise
5
Ž
.
Ä Ž
. 4
Ž
.
Ž
Ž
.
Ž
.
Ž
..
3
following the generation of highly reactive 17-electron complexes via photochemical electron transfer from 1b–d to the solvent. These
radical cations either undergo H-abstraction at the carbyne carbon followed by H-shift to form the dienes or they undergo exchange of
Cly for the CO ligand and Cl-abstraction at the metal to yield 8b–d. The product ratios reflect partitioning of the 17-electron species
between reactivity at the metal center vs. the carbyne carbon. q 1998 Elsevier Science S.A.
Keywords: Metal carbyne; Photooxidation; Metal radical; 17-Electron complex
1. Introduction
We previously reported that photolysis of the butenyl
5
Ž
.Ž
.
Ä
Ž
. 4
carbyne complex h –C5H5 CO P OMe Mo'C–
3
Ž
.
CH2CH2CH5CH2 1a in CHCl3 resulted in the for-
Ž
. w x
mation of cyclohexenone Scheme 1 1 . Mechanistic
studies on cyclohexenone formation were consistent
with a pathway initiated by electron transfer from the
carbyne complex to yield a radical cation. Hydrogen
abstraction at the carbyne carbon then generates a
Ž
.
cationic carbene 2a that undergoes an intramolecular
ene reaction to form the metallacycle 3a 1 . Next, CO
w x
insertion into the metallacycle ring of 3a, reductive
elimination and hydride shift yield cyclohexenone.
The minor organic product of this reaction is 1,4-pen-
Ž
.
tadiene Scheme 1 . The diene undoubtedly arises from
an alternative pathway for carbene 2a. Hydride shift
from C2 to C1 of the carbene ligand would yield the
h2-diene complex 4a, which would be prone to diene
loss under oxidative conditions. A related process has
Scheme 1.
)
been observed in complexes such as butyl carbyne 5
Corresponding author. Tel.: q1 352 3928768; Fax: q1 352
Ž
.
w x
Scheme 2 2 .
8460296; e-mail: lmwhite@chem.ufl.edu
0022-328Xr98r$19.00 q 1998 Elsevier Science S.A. All rights reserved.

(
)
14
K.E. Torraca et al.rJournal of Organometallic Chemistry 554 1998 13–18
Scheme 2.
Formation of cyclohexenone from the butenyl car-
byne 1a suggested that other alkenyl carbynes might
also form cyclic products via the mechanism in Scheme
5
Ž
1. For example, if the homologous series h –
.Ž Ž
.
Ä
Ž
.
4
Ž
.
C5H5 CO P OMe Mo'CCH2 CH2 nCH5CH2 n
3
Ž
.
Ž
.
Ž
..
s2 1b , 3 1c , and 4 1d were to undergo the same
sequence of reactions as 1a, the products would be
cycloheptenone, cyclooctenone and cyclononenone, re-
spectively.
Scheme 4.
The crucial step in the Scheme 1 mechanism is the
intramolecular ene reaction 2a™3a, in which the car-
bene moiety functions as the enophile. This is an ex-
tremely unusual mode of metal participation in the ene
reaction. In the extensively studied ‘metallo-ene reac-
2. Results and discussion
2.1. Synthesis of 1b–d
5
Ž
.Ž
Ž
.
Ä
Ž
Ž
. 4
3
The alkenyl carbynes h –C5H5 CO P OMe Mo
w x
tion,’ the metal either serves as the migrating group 3
Ž
.
Ž
.
.
'CCH2 CH2 nCH5CH2 ns2 1b , 3 1c and 4
w x
or catalyzes the ene reaction in an organic substrate 4 .
Ž
..
1d were synthesized by a deprotonationralkylation
Three types of intramolecular ene reaction have been
classified according to the pattern of connectivity be-
w x
strategy first reported by Green and Templeton 7 .
Deprotonation of methyl carbyne 6 with nBuLi and
subsequent alkylation of the resulting vinylidene anion
w x
tween ene and enophile 5 . The conversion of 2a to 3a
Ž
.
is an example of the type III ene reaction Scheme 3 , in
which the enophile is attached to the allylic terminus of
the ene.
Ž
.
Ž
.
with the alkenyl iodides I CH2 nCH5CH2 ns2–4
Ž
.
yielded the carbyne complexes 1b–d Scheme 5 . In
order to obtain good yields of pure products, care must
be taken to ensure that the alkenyl iodides are free of
protic impurities. In the presence of proton sources,
reprotonation of the vinylidene anion 7 results in regen-
eration of methyl carbyne 6 which is virtually insepara-
ble from the alkylated products. If the amount of 6 in
the reaction mixtures is minimal, 1b–d can be purified
by chromatography on neutral alumina. The pure car-
byne complexes 1b–d are yellow oils at room tempera-
ture and are thermally sensitive, thus requiring storage
in dry ether at y408C to avoid decomposition.
Type III intramolecular ene reactions are unusual, but
known examples in purely organic systems include ring
closure of a,v-dienes to yield 7-, 8-, and 9-membered
w
x
rings 5,6 . If the ring size dependence of the
organometallic system were similar, the homologous
alkenyl carbynes 1b–d could access the 7-, 8-, and
9-membered metallacycles 3b–d, respectively. Comple-
tion of the Scheme 1 pathway would then yield larger
Ž
.
cycloalkenones Scheme 4 .
This work is an examination of the photooxidation of
the alkenyl carbynes 1b–d. Although the chemistry of
these complexes exhibits significant differences from
that of 1a, the results lead to significant insight into the
radical cations arising from one-electron oxidation of
metal carbynes.
2.2. Photooxidation of 1b–d
Photolysis of 1b–d resulted in the production of both
organic and organometallic products. In order to iden-
tify the organic products, GC and H-NMR data for the
1
photolysis mixtures were compared with those from
corresponding authentic samples of the anticipated enone
and diene products. However, the GC and 1H-NMR
data for the products from 1b–d were not consistent
with the presence of enones. Instead, the dienes
Ž
.
CH2 5CH CH2 nCH5CH2 were the only identifiable
organic products that were derived from the original
Scheme 3.

(
)
K.E. Torraca et al.rJournal of Organometallic Chemistry 554 1998 13–18
15
2.3. Mechanistic considerations
Formation of the diene products upon photooxidation
of the alkenyl carbynes 1b–d has precedent in the
formation of 1,4-pentadiene as a minor product from the
Ž
photolysis of the butenyl carbyne 1a in CHCl3 Scheme
.
1 and Scheme 2 . Prior mechanistic studies on the
formation of organic products upon photooxidation of
metal carbynes are consistent with single electron trans-
fer from the carbyne excited state to the solvent as the
Ž
. w x
first step on the pathway Scheme 6 10 . Next, the
17-electron radical cation 9 abstracts hydrogen from the
reaction medium to form the cationic carbene complex
Scheme 5.
w x
w
x
2 2 . Diene formation results from 1,2 -H-shift in the
intermediate 2 to produce the h2-diene complex 4, in a
process related to Wagner–Meerwein shifts in organic
carbocations. Such rearrangements have previously been
carbyne substituents. They were accompanied by the
dichloromolybdenum carbynes 8b–d Scheme 6 . Car-
Ž
.
w
x
observed in electrophilic carbene complexes 11 . Under
the oxidative conditions of the photolysis, the h2-diene
complex 4 would be prone to loss of diene to yield the
free organic product.
In the chemistry of butenyl carbyne 1a Scheme 1 ,
the fate of cationic carbene complex 2a determines the
partitioning between diene and cycloalkenone products.
Although enone formation predominates from butenyl
carbyne 1a, the reaction fails for the longer alkenyl
chains derived from 1b–d. Formation of cycloalkenones
from 1b–d would require intramolecular ene reactions
from 2b–d. Although this process is favorable for 2a,
which produces the 6-membered metallacycle 3a, the
1
bynes 8b–d were identified by comparison to H-NMR
and 31 P-NMR spectra of authentic samples generated by
reaction of the alkenyl carbynes 1b–d with PCl5. Ow-
ing to the lability of 8b–d, pure samples could not be
Ž
.
isolated. However, the spectral data were in strong
agreement with the data from other h –
C5H5 Cl2 P OMe Mo'C–R complexes 2 , includ-
ing the 1-methylcyclopropyl derivative, for which a
5
Ž
.
Ä
Ž
.
4
w x
3
w x
crystal structure was obtained 8 .
5
Ž
T h e p h o t o o x i d a t i o n
.Ž
o f
h
–
.
Ä
Ž
.
4
Ž
.
C5 H5 CO P OMe Mo ' C–CH2 CH2 2CH5CH2
3
Ž
.
1b was carried out by irradiation in CDCl3 at 08C.
During the photolysis, the extent of starting material
1
loss was monitored by H-NMR. At about half conver-
sion of 1b, 1,5-hexadiene had been formed in 72% yield
1
as determined by GC analysis. Integration of the H-
NMR spectrum of the reaction mixture indicated a diene
yield of 73%, in excellent agreement with the GC value.
The corresponding dichloromolybdenum carbyne com-
plex 8b was formed in 17% yield as determined by
integration of the 1H-NMR spectrum. The yields are
reported at half-conversion of the carbyne because both
the dichloromolybdenum carbyne 8b and 1,5-hexadiene
are sensitive to the photolysis reaction conditions. For
example, at 33% conversion, the carbyne 1b had pro-
duced the dichloromolybdenum carbyne 8b in 25%
overall yield. By the time 47% conversion of 1b had
been reached, the yield of 8b had dropped to 17%. The
carbyne 1c was oxidized under the same conditions to
form 1,6-heptadiene in 72% yield and the dichloro-
molybdenum carbyne 8c in 21% yield as determined by
integration of the 1H-NMR spectrum of the reaction
mixture. Likewise, 1d formed 1,7-octadiene in 67%
yield and 8d in 17% yield. The presence of methyl
chloride was also observed in all of the reaction mix-
tures by 1H-NMR. Methyl chloride has been detected in
previous reactions of related complexes and is a product
Ž
.
w x
of Arbuzov reaction of the P OMe ligands 9 .
Scheme 6.
3

(
)
16
K.E. Torraca et al.rJournal of Organometallic Chemistry 554 1998 13–18
ene reaction is slower for systems which would form
larger rings. In these cases, the ene reaction cannot
organometallic one by about 4:1 under these reaction
conditions. The fact that both products are produced
provides a rare example in which both metal and carbon
radical reaction manifolds can be accessed from the
same species.
w
x
compete with the fast 1,2 -H shift that leads to diene
products.
Formation of the dichloromolybdenum carbynes
8b–d also has precedent. Dichloromolybdenum car-
bynes are minor products of most photolyses of similar
carbynes in CHCl3 and result from reactivity of the
initial 17-electron radical cation species 9 at the metal
3. Experimental section
Ž
.
center Scheme 6 . Rapid ligand exchange and halogen
atom abstraction are characteristic reactions of metal-
Standard inert atmosphere techniques were used
throughout. Hexane, petroleum ether, chloroform, and
methylene chloride were distilled from CaH2. Diethyl
ether and THF were distilled from NarPh2CO. All
NMR solvents were degassed by three freeze–pump–
thaw cycles. Benzene-d6 was vacuum transferred from
w
x
centered radicals 12–15 . If 9 undergoes these pro-
cesses instead of H-abstraction at the carbyne carbon,
dichloromolybdenum carbyne 8 is the final product. It
arises from chloride exchange at the metal center of 9 to
yield the radical compound 10 which undergoes halogen
abstraction to form 8. Although reversing the order of
the ligand exchange and halogen abstraction steps would
yield the same product, consideration of the relative
rates of these processes in other metal radical systems
˚
NarPh2CO. CDCl3 was stored over 3-A molecular
sieves. 4-Iodo-1-butene, 5-iodo-1-pentene and 6-iodo-
1-hexene were prepared from the corresponding tosy-
w
x
lates using the Finkelstein reaction 16 . Authentic sam-
ples of 1,5-hexadiene, 1,6-heptadiene, 1,7-octadiene, and
w
x
13 suggests the sequence shown in Scheme 6.
The formation of both the dienes and the dichloro-
2-cyclohepten-1-one were purchased from Aldrich.
5
Ž
.Ž
.
Ä
Ž
.
4
Ž .
h –C5H5 CO P OMe Mo'CCH3 6 was synthe-
3
w
x
molybdenum carbynes stems from partitioning of the
17-electron radical cation species 9b–d between ‘metal
radical’ and ‘organic radical’ behavior. Which product
is produced from this common intermediate depends on
the reactivity of the metal toward ligand exchange with
Cly vs. the tendency of the carbyne carbon to abstract
hydrogen. Because at least 85% of the starting material
can be accounted for in the form of organic dienes or
the dichloromolybdenum carbynes, these product ratios
allow an estimate of the preference for 9b–d to undergo
reaction at the metal vs. the carbyne carbon. Under
these reaction conditions, the dienes are produced pref-
erentially over the dichloromolybdenum carbynes by a
factor of about 4 to 1. Thus, hydrogen abstraction at the
carbyne carbon is faster than ligand exchange at the
metal center for the radical cations 9b–d, which have
sterically unhindered 18 alkyl substituents on the car-
byne ligands. These results can be contrasted with
carbynes bearing 38 substituents, for which H-abstrac-
tion is significantly slowed by steric hindrance and Cly
exchange to yield dichloromolybdenum carbynes domi-
sized as reported previously 1,17 . All other starting
materials were purchased in reagent grade and used
without further purification.
1H-, 31 P-, and 13C-NMR spectra were recorded on
Gemini-300 and VXR-300 NMR spectrometers. IR
spectra were recorded on a Perkin–Elmer 1600 spec-
trometer. GC was performed on an HP5890 chromato-
graph containing a 30 m=0.75 mm column of SPB-20
on fused silica. High resolution mass spectrometry was
performed by the University of Florida analytical ser-
vice.
Column chromatography was performed at 08C on
Ž
.
neutral alumina Brockmann Activity 1 . All photolyses
1
were performed at 08C and analyzed by H-NMR spec-
troscopy using decane as an internal standard. Irradia-
tion was done with a Hanovia medium pressure mercury
vapor lamp in a Pyrex immersion well.
3.1. Synthesis of alkenyl carbyne complexes
3 .1 .1 .
(
h
)
5 – C 5 H 5 C O P O M e
M o '
)( ) }
3
(
)
{
(
w
x
(
)
nates the reactivity 2,8 .
CCH2 CH2 2CH5CH2 1b
Ž
.
Methyl carbyne 6 175 mg, 0.514 mmol was dis-
2.4. Conclusion
solved in 15 ml of THF and allowed to react with a 2.3
Ž
M hexane solution of n-butyllithium 335 ml, 0.771
.
Ž
Although the photooxidation of the alkenyl carbynes
1b–d did not produce cycloalkenones, this chemistry
provides an interesting opportunity to assess the reactiv-
ity of the 17-electron radical cation species that are
produced upon photooxidation of metal carbynes. The
organic dienes and the dichloromolybdenum carbynes
produced in these photooxidations result from reactivity
of those radicals at the carbyne carbon and the metal
respectively. The organic product is favored over the
mmol at y788C. After 25 min, 4-iodo-1-butene 374
.
mg, 2.05 mmol was added. The solution was allowed
to react for 15 min at y788C and then warmed to room
temperature. Following removal of solvent in vacuo, the
residue was extracted with ether and chromatographed
on neutral alumina using 4:1 hexanerether as eluent
followed by 1:1 hexanerether after the 4-iodo-1-butene
was eluted. The product 1b was obtained as a yellow oil
Ž
.
145 mg, 71.5% after removal of solvent. For 1b:

(
)
K.E. Torraca et al.rJournal of Organometallic Chemistry 554 1998 13–18
17
1
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
H-NMR C6 D6 d 5.71 m, 1H, 5CH , 5.26 d, 5H,
s27 Hz , 241.7 d, CO, JPC s20 Hz , 139.1 5CH ,
.
Ž
.
Ž
Ž
.
Ž
.
Ž
.
Ž
C5H5, JPH s1 Hz , 4.99 m, 2H, 5CH2 , 3.38 d, 9H,
114.5 5CH2 , 91.0 C5H5 , 51.2 OMe , 50.0 Mo'
31
.
Ä1
4
Ž
.
.
Ž
.
Ž
OMe, JPH s12 Hz , 2.27 m, 2H, CH2 , 2.10 q, 2H,
CC , 34.0, 31.9, 29.0, 28.5 ppm; P H -NMR CDCl3
13
.
Ž
.
Ä1
4
Ž
.
s
d 203.9 ppm; IR CH2Cl2 1900 cmy1 nCO ; HRMS
Ž
.
Ž
.
CH2 , 1.63 p, 2H, CH2 ppm; C H -NMR C6 D6 d
98
q
Ž
.
Ž
Ž
Ž
.
Ž
.
Ž
.
315.9 d, Mo'C, JPC s28 Hz , 241.8 d, CO, JPC
FAB mrz calcd. for MqH
C17 H28 MoO4 P
.
Ž
.
.
Ž
.
18 Hz , 138.5 5CH , 115.1 5CH2 , 91.0 C5H5 ,
425.0784, found 425.0799.
31
Ž
.
Ž
.
Ä1
4
51.2 OMe , 49.4 Mo'CC , 33.3, 27.9 ppm; P H -
NMR CDCl3 d 203.8 ppm; IR CH2Cl2 1901 cm
Ž
Ž
y1
Ž
;
.
Ž
.
3.2. Synthesis of dichloromolybdenum carbynes
.
nCO
HRMS FAB m r z calcd. for Mq
Ž .
98
.
(
)
)
{
(
C15 H23 MoO4 P 396.0392, found 396.0387.
3 .2 .1 .
h
5 – C 5 H 5 C l 2 P O M e
M o '
) }
3
(
(
)
CCH2 CH2 2CH5CH2 8b
Alkenyl carbyne 1b 38.5 mg, 0.0976 mmol was
dissolved in 0.5 ml CDCl3 and allowed to react with
PCl5 20.0 mg, 0.0976 mmol at 08C. The solution
reacted for 1 min producing effervescence and was
characterized by NMR spectroscopy without further
5
(
)
)(
)
{
(
)
}
Ž
.
3.1.2.
CH2 CH2 3CH5CH2 1c
h – C 5 H5 C O P O M e
M o ' C –
3
(
(
)
Ž
.
Ž
.
Methyl carbyne 6 232 mg, 0.682 mmol was dis-
solved in 15 ml of THF and allowed to react with a 2.3
M hexane solution of n-butyllithium 445 ml, 1.02
Ž
1
.
Ž
mmol at y788C. After 25 min, 5-iodo-1-pentene 535
purification. The resulting H-NMR spectrum indicated
.
mg, 2.73 mmol was added. The solution was allowed
a mixture of compounds containing the dichloromolyb-
denum carbyne as the major component. Owing to the
lability of 8b, it could not be purified further. The NMR
signals of 8b were identified by comparison to the
spectral data of related compounds 2,8 . For 8b: H-
to react for 15 min at y788C and then warmed to room
temperature. Following removal of solvent in vacuo, the
residue was extracted with ether and then chromato-
graphed on neutral alumina using 4:1 hexanerether as
eluent followed by 1:1 hexanerether after the 5-iodo-
1-pentene was eluted. The product 1c was obtained as a
1
w
x
Ž
.
Ž
Ž
.
NMR CDCl3 d 5.95 d, 5H, C5H5, JPH s3 Hz , 5.78
Ž
.
.
.
Ž
m, 1H, 5CH , 5.01 m, 2H, 5CH2 , 3.92 d, 9H,
31
Ž
.
.
Ž
Ä1
4
yellow oil 198 mg, 71.1% after removal of solvent.
For 1c: H-NMR C6 D6 d 5.76 m, 1H, 5CH , 5.27
OMe, JPH s11 Hz , 3.18 m, 2H, CH2 ppm; P H -
1
Ž
.
Ž
.
Ž
.
NMR CDCl3 d 144.2 ppm.
Ž
Ž
Ž
.
Ž
.
d, 5H, C5H5, JPH s1 Hz , 4.99 m, 2H, 5CH2 , 3.39
5
.
Ž
.
(
)
{
(
)
}
d, 9H, OMe, JPH s12 Hz , 2.27 m, 2H, CH2 , 1.94
3.2.2.
(
h – C 5 H 5 C l2 P O M e
M o ' C –
3
.
4
Ž
.
Ž
.
)
(
)
q, 2H, CH2 , 1.56 p, 2H, CH2 , 1.43 p, 2H, CH2
CH2 CH2 3CH5CH2 8c
13
Ä1
Ž
.
Ž
Ž
.
ppm; C H -NMR C6 D6 d 316.2 d, Mo'C, JPC
Alkenyl carbyne 1c 11.5 mg, 0.0281 mmol was
dissolved in 0.5 ml CDCl3 and allowed to react with
.
Ž
.
Ž
Ž
.
s28 Hz , 241.7 d, CO, JPC s19 Hz , 138.9 5CH ,
Ž
.
Ž
.
Ž
.
Ž
.
114.6 5CH2 , 91.0 C5H5 , 51.2 OMe , 49.9 Mo'
PCl5 20 mg, 0.0281 mmol at 08C. The solution re-
acted for 1 min producing effervescence and was char-
acterized by NMR spectroscopy without further purifi-
cation. The resulting 1H-NMR spectrum indicated a
mixture of compounds containing the dichloromolybde-
num carbyne as the major component. Owing to the
lability of 8c, it could not be purified further. The NMR
31
.
Ä1
4
Ž
.
CC , 33.8, 28.5, and 28.1 ppm; P H -NMR CDCl3
d 203.8 ppm; IR CH2Cl2 1900 cmy1 nCO ; HRMS
Ž
.
Ž
.
98
Ž
.
qŽ
.
FAB mrz calcd. for M C16 H25 MoO4 P 410.0549,
found 410.0557.
5
(
)
)(
)
{
(
)
}
3.1.3.
CH2 CH2 4CH5CH2 1d
h – C 5 H5 C O P O M e
M o ' C –
3
(
(
)
signals of 8c were identified by comparison to the
spectral data of related compounds 2,8 . For 8c: H-
1
Ž
.
w
x
Methyl carbyne 6 180 mg, 0.529 mmol was dis-
Ž
.
Ž
Ž
.
solved in 15 ml of THF and allowed to react with a 2.3
M hexane solution of n-butyllithium 346 ml, 0.795
NMR CDCl3 d 5.95 d, 5H, C5H5, JPH s3 Hz , 5.79
Ž
Ž
.
.
.
Ž
m, 1H, 5CH , 4.97 m, 2H, 5CH2 , 3.91 d, 9H,
31
.
Ž
.
Ž
Ä1
4
mmol at y788C. After 25 min, 6-iodo-1-hexene 446
OMe, JPH s11 Hz , 3.17 m, 2H, CH2 ppm; P H -
.
Ž
.
mg, 2.12 mmol was added. The solution was allowed
NMR CDCl3 d 144.3 ppm.
to react for 15 min at y788C and then warmed to room
temperature. Following removal of solvent in vacuo, the
residue was extracted with ether and then chromato-
graphed on neutral alumina using 4:1 hexanerether as
eluent followed by 1:1 hexanerether after the 6-iodo-
1-hexene had eluted. The product 1d was obtained as a
5
(
)
)
{
(
)
}
3.2.3.
(
h – C 5 H 5 C l2 P O M e
M o ' C –
3
(
)
CH2 CH2 4CH5CH2 8d
Alkenyl carbyne 1d 33.5 mg, 0.0793 mmol was
dissolved in 0.5 ml CDCl3 and allowed to react with
PCl5 16.5 mg, 0.0793 mmol at 08C. The solution
reacted for 1 min producing effervescence and was
characterized by NMR spectroscopy without further
Ž
.
Ž
.
Ž
.
yellow oil 169 mg, 75.6% after removal of solvent.
1
Ž
.
Ž
.
For 1d: H-NMR C6 D6 d 5.76 m, 1H, 5CH , 5.28
1
Ž
Ž
Ž
.
Ž
.
d, 5H, C5H5, JPH s1 Hz , 5.00 m, 2H, 5CH2 , 3.40
purification. The resulting H-NMR spectrum indicated
.
Ž
.
d, 9H, OMe, JPH s12 Hz , 2.27 m, 2H, CH2 , 1.97
a mixture of compounds containing the dichloromolyb-
denum carbyne as the major component. Owing to the
lability of 8d, it could not be purified further. The NMR
.
4
Ž
Ž
.
Ž
.
q, 2H, CH2 , 1.57 p, 2H, CH2 , 1.30 m, 4H, CH2
13
Ä1
.
Ž
ppm; C H -NMR C6 D6 d 316.4 d, Mo'C, JPC

(
)
18
K.E. Torraca et al.rJournal of Organometallic Chemistry 554 1998 13–18
signals of 8d were identified by comparison to the
diene product at half conversion. In order to remove the
starting alkenyl carbyne 1b, the final reaction mixture
was cannulated onto a pipette column of alumina under
N2. The organics were rinsed off the column with
pentane into a 5-ml volumetric flask. The flask was
filled to the line with pentane and mixed well. The yield
of the diene was calculated from the integration of the
GC trace of the resulting mixture.
1
w
x
spectral data of related compounds 2,8 . For 8d: H-
Ž
.
Ž
.
NMR CDCl3 d 5.94 d, 5H, C5H5, JPH s3 Hz , 5.79
Ž
.
Ž
.
.
Ž
m, 1H, 5CH , 4.95 m, 2H, 5CH2 , 3.91 d, 9H,
OMe, JPH s11 Hz , 3.16 m, 2H, CH2 ppm; P H -
31
.
Ž
Ä1
4
Ž
.
NMR CDCl3 d 144.3 ppm.
3.3. Photooxidation of alkenyl carbynes
The yield of the dienes was determined by integra-
tion of the H-NMR spectrum and compared to the GC
1
5
(
)(
)
{
(
) }
3.3.1. Photooxidation of h –C5 H5 CO P OMe 3 Mo
(
)
( )
'CCH2 CH2 2CH5CH2 1b
analysis. Given the close agreement of the GC and
NMR values for diene yield from 1b and the difficulty
of quantitatively separating the carbyne complexes from
the organic products, only the yields based on the
1H-NMR integration are reported for the photooxidation
of the alkenyl carbynes 1c–d.
Ž
.
Carbyne 1b 60 mg was dissolved in 1 ml of
CDCl3, and 1.6 ml of decane was added as the internal
standard for GC analysis. An NMR tube was charged
with this mixture. The reaction mixture was photolyzed
at 08C while the progress of the reaction was monitored
1
by H-NMR. The photolysis was stopped at approxi-
mately half conversion of 1b. 1,5-hexadiene was formed
Acknowledgements
in 72% yield as determined by GC analysis. Integration
of the H-NMR spectrum led to a value of 73% yield.
1
Financial support of this work was provided by the
National Science Foundation Grant CHE-9421434 . We
thank Ken Lo for assistance with the GC experiments.
The corresponding dichloromolybdenum carbyne com-
5 – C 5 H
C l 2 P O M e
Ž
.
Ž
.
Ä
Ž
.
4
M o '
3
p le x
h
.
Ž
5 Ž
.
CCH2 CH2 2CH5CH2 8b was formed in 17% yield
1
as determined by integration of the H-NMR spectrum.
5
References
(
)(
)
{
(
) }
3.3.2. Photooxidation of h –C5 H5 CO P OMe 3 Mo
(
)
( )
'C–CH2 CH2 3CH5CH2 1c
w x
1
M.D. Mortimer, J.D. Carter, L. McElwee-White,
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When photolyzed as described for 1b, carbyne 1c
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c a rb y n e c o m p le x
C5H5 Cl2 P OMe Mo'CCH2 CH2 3CH5CH2 8c
in 21% yield as determined by integration of the H-
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Ž
.
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2
T.K. Schoch, S.D. Orth, M.C. Zerner, K.A. Jørgensen, L.
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m o ly b d e n u m
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–
.
Ž
.
.
Ä
Ž
.
4
Ž
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Ž
w x
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Ž
.
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1
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Ž
.
1978 476.
5
(
)(
){
(
) }
3.3.3. Photooxidation of h –C5 H5 CO P OMe 3 Mo
w x
Ž
.
6
H.M.R. Hoffmann, Angew. Chem. Int. Ed. Engl. 8 1969 556.
(
)
( )
w x Ž .
'C–CH2 CH2 4CH5CH2 1d
7
a
D.C. Brower, M. Stoll, J.L. Templeton, Organometallics 8
.
Ž
Ž .
1989 2786.
Morton, A.G. Orpen, J. Chem. Soc. Dalton Trans. 1991 3021.
Ž .
b R.G. Beevor, M.J. Freeman, M. Green, C.E.
When photolyzed as described for 1b, carbyne 1d
formed 1,7-octadiene in 67% yield and the dichloro-
c a rb y n e c o m p le x
C5 H5 Cl2 P OMe Mo ' C–CH 2 CH 2 4CH5CH 2
Ž
.
c R.G. Beevor, M.J. Freeman, M. Green, C.E. Morton, A.G.
5
Ž
m o ly b d e n u m
h
–
Ž
.
Orpen, J. Chem. Soc. Chem. Commun. 1985 68.
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.
Ä
Ž
.
4
Ž
.
w x
8
3
Ž
.
Ž
.
8d in 17% yield as determined by integration of the
1H-NMR spectrum.
w x
9
K.B. Kingsbury, J.D. Carter, A. Wilde, H. Park, F. Takusagawa,
L. McElwee-White, J. Am. Chem. Soc. 115 1993 10056.
Ž
.
w
w
x
Ž
.
10 L. McElwee-White, Synlett 1996 806.
3.4. GC analysis of reaction products from 1b
x
11 C. Roger, G.S. Bodner, W.G. Hatton, J.A. Gladysz,
Ž
.
Organometallics 10 1991 3266.
w
w
x
A standard calibration curve was prepared for obtain-
ing the concentration of the diene product from the area
obtained from the GC integration. The reaction mixture
was prepared as described above. Before starting the
photolysis, GC was performed on the reaction mixture.
As indicated by the GC, the diene product is detectable
before the photolysis takes place. This, coupled with the
12 D. Astruc, Electron Transfer and Radical Processes in Transi-
tion-Metal Chemistry, VCH, 1995.
x
Ž
.
13 W.C. Trogler Ed. , Organometallic Radical Processes, Elsevier,
1990.
w
w
w
x
Ž
.
14 D. Astruc, Accts. Chem. Res. 24 1991 36.
x
Ž
.
15 M. Baird, Chem. Rev. 88 1988 1217.
x Ž .
16 a L.F. Fieser, M. Fieser, Reagents for Organic Synthesis, Vol.
Ž .
1, John Wiley, 1967, p. 1179.
b L.F. Fieser, M. Fieser,
1
Reagents for Organic Synthesis, Vol. 1, John Wiley, 1967, p.
1088.
absence of diene peaks in the starting H-NMR indi-
cates that the diene product is formed from 1b in the
injection port of the GC. Hence, 1b had to be removed
from the reaction mixture to obtain accurate yields of
w
x Ž .
17 a G.A. McDermott, A.M. Dorries, A. Mayr, Organometallics 6
Ž
.
Ž .
b A. Mayr, A.M. Dorries, G.A. McDermott, D.
1987 925.
Van Engen, Organometallics 5 1986 1504.
Ž
.